You might want to consider using parts for outside yard lights made by a company called Malibu. They use press in bulbs rather than the screw in type. They are very inexpensive and you can work them off a low voltage transformer. Another option is to use miniture christmas tree lights. Their cost is almost nothing. You can pick up a string of 100 lights during the after christmas sales for about $1. You just take the strings apart and individually wire them in your buildings. You just twist the ends of the wires together for each side of the circuit. Cover with a small piece of electrical tape and they will last for a long time. If you use colored lights the blue, green, orange and red can give you some nice night time effects.
John